Digital subtraction angiography (DSA) is an X-ray imaging method which removes background structures from the final image. A mask image containing the background structures is acquired. Subsequently, contrast medium is injected. An image is then acquired of blood vessels and of perfused tissues containing the contrast medium. The mask image is subtracted from the image containing the injected blood vessels and perfused tissues. In this way, there is improved contrast between blood vessels or tissues, and their background.
U.S. Pat. No. 4,729,379 discusses digital subtraction angiography. Unfortunately, the DSA technique is less useful in cardiac procedures, because it is sensitive to patient motion.